"A 15-km-long E-W ridge forming the border between Chile and Bolivia is comprised of several stratovolcanoes with Holocene lava flows. Andesitic-dacitic lava flows extend as far as 5 km north from the active crater of Volcán Olca and to the north and west from vents farther to the west. Olca is flanked on the west by Cerro Michincha and on the east by Volcán Paruma, which is immediately west of the higher pre-Holocene Cerro Paruma volcano. Volcán Paruma has been the source of conspicuous fresh lava flows, one of which extends 7 km to the SE. Volcán Paruma has displayed persistent fumarolic activity in recent years. The only known historical activity from the Olca-Paruma complex was a flank eruption of unspecified character between 1865 and 1867." -Smithsonian Volcano Archive